In recent years, the welding market has required increasing a speed of welding or reducing spatters. Welding at a higher speed will increase the number of work-pieces welded, while a reduction of spatters will decrease the number of steps in post treatments to remove spatters attached. Achievement of these requirements allows carrying out a quality welding steadily, which results in improving the welding productivity.
A conventional welding device elaborately controls as many as several hundred types of waveform controlling parameters in order to improve the stability of high quality welding. The waveform controlling parameters have an optimum value for respective welding conditions. Setting of a variety of welding conditions will thus search an appropriate waveform controlling value from a welding condition table stored in a data memory of the welding device for controlling the waveform. The welding condition includes, e.g. a wire diameter, a type of shield gas, a method of welding, a welding current value, or a length of wire supplied per unit time (hereinafter referred to as “wire supplying speed”). The foregoing art is disclosed in, e.g. Reference Patent Document 1.
However, an operator in the field must adjust a distance between a feeder of a welding tip and a work-piece (hereinafter referred to as a feeder-work-piece distance). This distance is one of important factors for selecting a waveform controlling parameter. A welding device manufacturer thus sets a feeder-work-piece distance of general purpose, then selects a waveform controlling parameter, and stores it in the welding condition. This is done in general among the welding device manufacturers.
For instance, when a target spot to be welded of a work-piece is close to a welding jig in the field, the welding jig sometimes interferes with (or hits) a welding torch. In this case, the torch must remove from the work-piece in order to avoid the interference. Then an actual feeder-work-piece distance sometimes becomes longer than the set one. When a gap exists between the work pieces, it is necessary to reduce a deviation from a welding target as little as possible. In such a case, an actual feeder-work-piece distance sometimes becomes shorter than the set one.
In these cases discussed above, although the feeder-work-piece distance is changed, the welding condition remains unchanged. Use of a welding wire having a higher resistance such as soft steel or stainless steel will greatly change a resistance at a welding output path in response to a change in the feeder-work-piece distance. A wire supplying speed is thus not changed, but an output current or an appropriate welding voltage is changed, so that the welding cannot be done properly. That is because the welding waveform parameters have been set in conjunction with respective wire supplying speeds or respective set values of welding current. For instance, when the actual feeder-work-piece distance becomes greater than the set one, the output welding current decreases, and the waveform controlling parameter stays unchanged although the current decreases. As a result, the spatters increase. On top of that, a voltage corresponding to the prolonged section of the welding wire is not supplied, so that the welding voltage becomes short, and as a result, the arc becomes unstable.
The welding cannot be done appropriately not only in a main welding period but also at arc starting time, so that the arc becomes unstable at the arc starting time, and it takes a time before the arc becomes stable.
Reference Patent Document 1: Unexamined Japanese Patent Publication No. H09-122914